1. Field of the Invention
The present invention relates to a disk cartridge and a disk drive, and, more particularly, to a magnetic disk cartridge which accommodates a flexible magnetic disk having a metallic center hub within a plastic thin case. The present invention further relates to a disk drive preferable at least for driving the flexible magnetic disk of the stated magnetic disk cartridge.
2. Description of the Related Art
A flexible magnetic disk, called a "floppy disk", can be classified into two types, at present, a flexible magnetic disk accommodated in a flexible jacket; and a disk cartridge type magnetic disk accommodated in a thin and relatively rigid case.
The magnetic disk of the former type is provided with no center hub so that the magnetic disk is rotated by being held at a portion around a center hole thereof between a hollow end of a spindle member and a vertically-movable clamp member of a disk drive. Therefore, the accuracy in centering the magnetic disk can be, in principle, determined by the accuracy in machining the center hole in the disk and an expansion/contraction of the disk caused by temperature and humidity. However, this accuracy in machining the center hole involves a certain restriction to be improved because this magnetic disk needs to be smoothly loaded/unloaded. On the other hand, the centering accuracy due to the expansion caused from the changes in temperature and humidity can be, to a certain extent, compensated by the temperature and humidity correction in the disk drive. However, in a case where the magnetic disk is cut out from a web-like recording medium, the anistropy in expansion/contraction of the recording medium remains, i.e. The degree of expansion/contraction of the recording medium in the direction along which the film has been wound is different from that in the widthwise direction of the same. Therefore, a problem arises that the deformation of the track of the magnetic disk cannot be prevented simply by the temperature and humidity correction or compensation features in the disk drive.
On the other hand, the latter disk cartridge type magnetic disk is provided with a hard center hub for chucking. Although various type of center hubs for various type of chucking have been proposed, the metal plate type are predominant at present, most of which utilize magnetic attraction and a drive pin as a driving system. In the magnetic disk having such a center hub, dimensional accuracy of the inner diameter of the hub is not required to be very high. Therefore, it can be subjected to a heat treatment for the purpose of correcting the distortion or strain thereof. For example, in a case of a magnetic disk derived from a base film made from polyethylene-terephthalate, the anistropic expansion/contraction of the disk can be reduced to one-third by punching it into a disc-like form and then leaving it at an ambient temperature of 80.degree. C. Therefore, the deformation of the track after assembly can be considerably reduced.
FIGS. 9 and 10 respectively illustrate an essential part of a magnetic disk having a metallic center hub and the essential part of a magnetic disk drive.
Referring to the drawings, a thin plastic case assembly 100 comprises an upper case 101 and a lower case 102. The lower case 102 has a center opening 103. A flexible magnetic disk 104 is arranged in such a manner that the marginal portion around the center opening 103 is secured to a metallic center hub 105. The disk 104 is freely rotatably accommodated in the case assembly 100. The center hub 105 has a drive hole 106, and a lower surface thereof to which an annular projection 107 is secured, the annular projection 107 including straight portions 108 in the inner surface thereof.
The magnetic disk drive is provided with a spindle member (rotary driving member) 109 for chucking and rotating the center hub 105. The spindle member 109 has a magnet 110 to attract and hold the rear side of the center hub 105. In addition, a drive pin 111 is inserted into and engaged with the drive hole 106. Furthermore, the outer surface of the spindle member 109 is engaged with the inner surface of the annular projection 107, as shown by an imaginary line in FIG. 9A, so that the spindle member 109 can correctly position the center hub 105 during rotational drive of the magnetic disk 104.
In the above-described structure, when the magnetic disk cartridge is loaded on the disk drive, the lower case 102 of the case assembly 100 is positioned by a support member 112 so that a predetermined gap can be left between the center hub 105 chucked by the spindle member 109 and the inner surface 101a of the upper case 101. However, if the case assembly 100 is deformed, the top portion of the drive pin 111 may be brought into contact with the inner surface 101a of the upper case 101, causing smooth rotation of the magnetic disk 104 to be prevented or disturbed.
Therefore, an attempt has been made, as shown in FIG. 11, to provide a projection 113, which can be brought into contact with the inner surface 101a of the upper case 101 in the central portion of the center hub 105, for the purpose of preventing the drive pin 111 from being brought into contact with the upper case 101, even if the case assembly 100 deforms.
However, if the upper case 101 is warped or curved inward in the structure shown in FIG. 11, the projection 113 will always contact the inner surface 101a of the upper case 101. This contact will serve as a load against rotation, and causes the upper case 101 to be abraded, resulting in the generation of abrasion dust. In addition, there is the fear that the forced contact pressure between the center hub 105 and the end surface of the spindle 109 will becomes too high to allow the appropriate centering of the disk 104 with respect to the spindle 109. Furthermore, because the height of the projection 113 should be made higher than the drive pin 111 by a certain degree, the inner thickness S of the case assembly 100 can not be sufficiently reduced, i.e. the case assembly 100 can not be made thin to the degree desired.
On the other hand, the disk drive for the disk cartridge is provided with only the center hub chucking function, and is not arranged to drive the magnetic disk accommodated in the jacket, without the center hub 105.